Study of Al and Ga Doped and Co-Doped ZnO Thin Film as front Contact in CIGS Solar Cell

Abstract

Zinc Oxide (ZnO) is a group II-VI semiconductor material widely applied in optoelectronic because of its wide band gap (~ 3.3 eV), high chemical stability, high order transmittance and piezoelectric properties. In the present study Al doped ZnO, Ga doped ZnO and Al and Ga (1:1) co-doped ZnO thin films were grown on glass substrates by DC sputtering at room temperature. The thickness for all the deposited film was kept constant. The transmission of Al doped ZnO and Al and Ga co-doped ZnO the films shows more than 80 % of transmittance in the visible region of light where as for Ga doped ZnO thin film around 75 % of transmittance was observed. The XRD pattern of the films shown a preferable growth orientation in (002) phase, except this main peak some weak peaks were also appeared at (102) and (103). It shows the films are polycrystalline in nature. Also from the XRD result the crystallite size of Al doped ZnO, Ga doped ZnO and Al and Ga co-doped ZnO were determined and found to be 63.2, 73.3 and 85.5 nm respectively. Also from FTIR, the increase in crystallanity is observed in case of Al doped ZnO and Al and Ga (1:1) co-doped ZnO thin film. The electrical properties such as mobility, carrier concentration and resistivity were measured using Hall Effect Measurement system. Both carrier concentration and mobility values were increased in case of Al and Ga co-doped ZnO thin film compared to that of doped ZnO thin films. In case of Al and Ga co-doped ZnO thin film the lowest resistivity value of 5.46 × 10⁻⁴ Ω cm was observed. It was observed that Al and Ga co-doped ZnO thin film showed the resistivity in the range of 10⁻⁴ Ω cm with enhanced optical transmittance. Such a transparent and conducting zinc-oxide thin film can be used as front contact in CIGS solar cell.